A step charging method of a lithium battery

Abstract

The application discloses a stepped charging method of a lithium battery, which comprises the following steps: performing constant-current rapid charging on a battery module; judging whether the highest single-body voltage in the battery module is greater than the capacity voltage inflection point of the battery cell and whether the maximum voltage difference in the battery module is greater than a preset voltage difference; if yes, entering a constant-voltage equalization charging process; if no, entering a stepped charging process. Under the premise of ensuring the charging speed by adjusting the charging voltage and current according to the charging state, the application prolongs the duration at the end of the charging process, prolongs the effective equalization time as much as possible without affecting the normal use of customers, realizes a better equalization effect, and guarantees the consistency of the battery cells of the battery module as much as possible.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, and in particular to a stepped charging method for lithium batteries. Background Technology

[0002] With the increasing scarcity of traditional energy sources such as oil and coal, and the growing awareness of environmental protection, lithium batteries, as a green, safe, and environmentally friendly new energy source, have been widely used in our lives and work, such as in power, energy storage, and backup power applications, including small power applications such as sightseeing vehicles, patrol vehicles, and forklifts.

[0003] Compared to conventional nickel-metal hydride batteries, lithium-ion batteries have significant advantages such as high operating voltage, high energy density, low self-discharge rate, and no memory effect. However, lithium-ion batteries also have disadvantages such as poor cell uniformity, inability to withstand overcharging, and inability to withstand over-discharging. When charging a lithium-ion battery, an upper charging voltage limit needs to be set. When the highest cell voltage or total voltage rises to the upper limit threshold, the battery control system will limit the power and implement protection measures. Similarly, when discharging, a lower discharge voltage limit needs to be set. When the lowest voltage or total voltage drops to the lower discharge threshold, the battery control system will also issue an alarm, limit the power, and implement protection measures.

[0004] For lithium batteries, current charging control strategies mainly include constant current / constant voltage charging and stepped charging. Constant current / constant voltage charging initially charges the battery module with a constant current while the charging voltage slowly increases until it reaches the charging cutoff voltage. Afterward, the battery is charged with a constant cutoff voltage, maintaining the charging voltage while the charging current slowly decreases until charging stops when the charging current drops to the set cutoff current. Stepped charging optimizes constant current / constant voltage charging by setting multiple current-reducing voltage points in the later stages of charging, performing multiple stages of current-reducing charging.

[0005] The above charging control strategies all use fixed charging current and charging voltage. When the consistency of the lithium battery modules is relatively good, they can basically ensure that the system can charge safely and stably. However, when the consistency of the battery modules becomes poor as the number of cycles increases, good charging effect cannot be achieved. The battery modules often quickly trigger the overvoltage protection of individual cells due to uneven cell voltage.

[0006] The consistency of lithium-ion battery modules refers to the uniformity of voltage, charge, capacity, degradation rate, internal resistance and its rate of change over time, lifespan, temperature influence, and self-discharge rate and its rate of change over time when the modules are composed of lithium-ion battery cells of the same specification. Individual cells within the same type and specification of lithium-ion battery module may differ in parameters such as voltage, internal resistance, and capacity. When used in a lithium-ion battery module, the performance indicators often fail to reach the original levels of the individual battery cells.

[0007] Lithium-ion battery modules primarily rely on a passive balancing circuit on the protection board to discharge high-voltage cells during charging, thereby achieving consistent battery capacity. However, because the remaining capacity of a cell is not entirely consistent with its voltage, and the voltage acquisition by the protection board is also subject to error, passive balancing is only performed towards the end of charging when the voltage difference between cells is relatively large, in order to ensure the accuracy of balancing. Due to the short charging time at the end of the current charging control strategy, the balancing time is short, resulting in unsatisfactory performance and failing to effectively solve the problem of inconsistent cell capacity within the module. Summary of the Invention

[0008] This invention proposes a stepped charging method for lithium batteries to solve the above-mentioned technical problems.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A stepped charging method for lithium batteries includes the following steps:

[0011] Step 1, with the charging request voltage V = V max Charging request current I = I max The battery module is subjected to constant current fast charging, where V max For the maximum requested charging voltage, I max Maximum requested charging current;

[0012] Step 2: Determine whether the highest single-cell voltage within the battery module is greater than the capacity voltage inflection point V of the cell. g And whether the maximum pressure difference within the battery module is greater than the preset pressure difference V diff If so, it will enter the constant voltage equalization charging process, with a charging voltage requirement of V = V. chg V chg This is the charging output voltage value of the charger; otherwise, it enters the stepped charging process.

[0013] Step 3, during the stepped charging process, a first current-reducing voltage V is preset. dp1 Second current-dropping voltage V dp2 Third current-dropping voltage V dp3 When the battery module voltage V0 ≥ V dp1 At that time, the charging request current When the battery module voltage V0 ≥ V dp2 At that time, the charging request current When the battery module voltage V0 ≥ V dp3 At that time, the charging request current I = I min I min Minimum charging request current;

[0014] Step 4: If charging stops, exit charging; otherwise, return to step 2.

[0015] Preferably, step 2 of the constant voltage equalization charging process further includes the following steps:

[0016] Step 21: Determine whether the maximum pressure difference within the battery module is greater than the preset pressure difference V. diff If it is 1 / 2, then the charging request voltage V increases by 1V;

[0017] Step 22: Determine whether the charging request voltage V is greater than the maximum requested charging voltage V. max If so, then the charging voltage V = V max .

[0018] Preferably, the first current-reducing voltage V dp1 Second current-dropping voltage V dp2 Third current-dropping voltage V dp3 The values ​​were set to 3500mV, 3550mV, and 3600mV respectively.

[0019] Preferably, when a fault alarm indicating that charging is not allowed is received during the charging process in steps 1 to 4, the charging request voltage V = 0, the charging request current I = 0, and charging is stopped.

[0020] Preferably, the fault alarm that prevents charging includes one or more of the following: cell voltage too high, cell temperature too high, cell fault, and BMS board fault.

[0021] Compared with existing technologies, this invention extends the duration of the final charging period by adjusting the charging voltage and current to ensure charging speed. This can extend the effective balancing time as much as possible without affecting normal use by customers, thereby achieving a better balancing effect and ensuring the consistency of battery module cells as much as possible. Attached Figure Description

[0022] Figure 1 This is a flowchart of a stepped charging method for a lithium battery according to the present invention;

[0023] Figure 2 This is a flowchart of the constant voltage equalization charging process in a stepped charging method for lithium batteries according to the present invention. Detailed Implementation

[0024] The present invention will now be described in detail with reference to the specific embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0025] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular forms “a,” “the,” and “the” used in this invention and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0026] This invention provides a stepped charging method for lithium batteries. First, through extensive experimental testing, the capacity-voltage inflection point V of the battery cell is determined. g Before the inflection point, there is a constant current fast charging phase; after the inflection point, there is a stepped charging phase at the end of the charging process. After the fast charging phase, the remaining capacity of the battery module can generally reach over 95%. At this point, if the customer needs to use it, they can use it directly without having to wait a long time for less than 5% of capacity remaining. However, if the customer does not need to use it in the short term, the small power battery module can continue with stepped charging. After entering stepped charging, the charging control strategy will control the charging current and charging voltage based on factors such as the highest body voltage and total voltage, extending the equalization time at the end of the charging process. This better maintains the consistency of the battery module.

[0027] like Figure 1 As shown, the specific steps of the present invention are as follows:

[0028] Step 1, with the charging request voltage V = V max Charging request current I = I max The battery module is subjected to constant current fast charging, where V max For the maximum requested charging voltage, I max This is the maximum requested charging current.

[0029] Step 2: Determine whether the highest single-cell voltage within the battery module is greater than the capacity voltage inflection point V of the battery cell. g And whether the maximum pressure difference within the battery module is greater than the preset pressure difference V diff If so, it will enter the constant voltage equalization charging process, with a charging voltage requirement of V = V. chg V chg This is the charging output voltage value of the charger; otherwise, it enters the stepped charging process.

[0030] Step 3, during the stepped charging process, a first current-reducing voltage V is preset. dp1 Second current-dropping voltage V dp2 Third current-dropping voltage V dp3 When the battery module voltage V0 ≥ V dp1 At that time, the charging request current When the battery module voltage V0 ≥ V dp2 At that time, the charging request current When the battery module voltage V0 ≥ V dp3 At that time, the charging request current I = I min I min This is the minimum charging request current.

[0031] Step 4: If charging stops, exit charging; otherwise, return to step 2.

[0032] During charging, the battery module voltage is continuously monitored to determine its consistency. If the battery module's consistency is good, the charging control process will reduce the current three times based on the battery module voltage until the battery module is fully charged. If the battery module's consistency is poor, the charging control process will perform constant voltage equalization charging to slow the voltage rise rate and extend the charging time. In the above steps, the preset voltage difference V... diff First current-dropping voltage V dp1 Second current-dropping voltage V dp2 Third current-dropping voltage V dp3 The charging curve obtained from the battery cell can be set as needed based on different testing items. Specifically, the first current-reducing voltage V dp1 Second current-dropping voltage V dp2 Third current-dropping voltage V dp3 The values ​​were set to 3500mV, 3550mV, and 3600mV respectively.

[0033] like Figure 2 As shown, step 2, the constant voltage equalization charging process may include the following steps:

[0034] Step 21: Determine whether the maximum pressure difference within the battery module is greater than the preset pressure difference V. diff If it is 1 / 2, then the charging request voltage V increases by 1V;

[0035] Step 22: Determine whether the charging request voltage V is greater than the maximum requested charging voltage V. max If so, then the charging voltage V = V max .

[0036] With continued use, the consistency of the battery module will deteriorate. Once the battery module enters the stepped charging phase, it will continuously monitor the maximum voltage difference within the battery pack. If the maximum voltage difference exceeds the preset voltage difference V... diff Then the battery module enters the constant voltage equalization charging process. The battery module will first read the charging output voltage value V of the charger through communication. chgAs the charging request voltage, the charging voltage is prevented from increasing further, while the charging current gradually decreases. When the charging current decreases to a certain level, the higher-voltage cells will be pulled down due to the balancing process, while the lower-voltage cells will have their voltage increased because they are not balancing. This reduces the maximum voltage difference within the battery module. When the maximum voltage difference within the battery module decreases to a preset voltage difference V... diff When it is less than 1 / 2, the charging request voltage is at the original charging request voltage V. chg Increase the voltage by 1V from the base voltage until the charging request voltage reaches the maximum charging request voltage V. max Then stop.

[0037] Furthermore, when a fault alarm indicating that charging is not allowed is received during the charging process in steps 1 to 4, the charging request voltage V = 0, the charging request current I = 0, and charging is stopped. Here, the fault alarm indicating that charging is not allowed includes one or more of the following: cell voltage too high, cell temperature too high, cell fault, BMS board fault, etc.

[0038] Other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of the invention are indicated by the claims of this application.

[0039] It should be understood that the present invention is not limited to the precise structure described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A stepped charging method for lithium batteries, characterized in that, Includes the following steps: Step 1, request charging voltage Charging request current The battery module is subjected to constant current fast charging, among which... For the maximum requested charging voltage, Maximum requested charging current; Step 2: Determine whether the highest single-cell voltage within the battery module is greater than the capacity voltage inflection point of the battery cell. And whether the maximum pressure difference within the battery module is greater than the preset pressure difference. If so, it will enter the constant voltage equalization charging process, and the charging voltage requirement will be [not specified]. , This is the charging output voltage value of the charger; otherwise, it enters the stepped charging process. Step 3, during the stepped charging process, a first current-reducing voltage is preset. Second step-down voltage Third step-down voltage When the battery module voltage At that time, the charging request current When the battery module voltage At that time, charging request current When the battery module voltage At that time, charging request current , Minimum charging request current; Step 4: If charging stops, exit charging; otherwise, return to step 2. Step 2 of the constant voltage equalization charging process also includes the following steps: Step 21: Determine whether the maximum pressure difference within the battery module is greater than the preset pressure difference. 1 / 2, if so, then the charging voltage is required. Increase by 1V; Step 22, determine the charging request voltage Is it greater than the maximum requested charging voltage? If so, then the charging voltage is required. .

2. The step-charging method for a lithium battery according to claim 1, characterized in that, First current reduction voltage Second step-down voltage Third step-down voltage The values ​​were set to 3500mV, 3550mV, and 3600mV respectively.

3. The step-charging method for a lithium battery according to claim 1, characterized in that, When a fault alarm indicating that charging is not allowed is received during the charging process in steps 1 to 4, the charging request voltage is... Charging request current Stop charging.

4. The step-charging method for a lithium battery according to claim 3, characterized in that, The fault alarms that prevent charging include one or more of the following: cell voltage too high, cell temperature too high, cell fault, and BMS board fault.

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